Weather index

The Iowa DOT uses a weather index to score the severity of the winter weather at each of its maintenance facilities. The index creates a higher score for locations that report longer events, more frequent events, colder temperatures and more snowfall. The duration and frequency of the different events are normalized by the Iowa expected extreme for each event, then scaled by an “importance” factor. High indices correlate to more severe winters.

The index is computed using the following information.

The number of:

Snow events

Freezing Rain events

Snowfall in inches

The number of hours of:

Snow

Mixed Precipitation

Freezing Rain

Blowing Snow

Sleet

The lowest pavement temperature observed during these precipitation events